Lithography techniques include processes in which, for example, a resist film formed from a resist material is formed on top of a substrate, the resist film is selectively exposed with irradiation such as light, an electron beam or the like through a mask in which a predetermined pattern has been formed, and then a developing treatment is conducted, thereby forming a resist pattern of the prescribed shape in the resist film.
Resist materials in which the exposed portions change to become soluble in a developing liquid are termed positive materials, whereas resist materials in which the exposed portions change to become insoluble in the developing liquid are termed negative materials.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used; however, nowadays, KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers, electron beams (EB), extreme ultraviolet radiation (EUV) and X-rays.
Resist materials are required to have lithography properties such as high sensitivity to the aforementioned light source and enough resolution to reproduce patterns with very fine dimensions.
As resist materials which fulfill the aforementioned requirements, a chemically-amplified resist is used containing: a base component that displays changed solubility in an alkali developing solution under action of an acid; and an acid generator that generates an acid upon exposure.
For example, as the chemically-amplified positive resist composition, a composition containing a resin component (a base resin) that exhibits increased solubility in an alkali developing solution under action of acid and an acid generator component is commonly used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, an acid is generated from the acid generator, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Resins (acrylic resins) that contain structural units derived from (meth)acrylate esters within the main chain thereof are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Documents 1 and 2).
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of an acrylate ester having a hydrogen atom bonded to the α-position and a methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of an acrylate having a hydrogen atom bonded to the α-position and a methacrylate having a methyl group bonded to the α-position.
Also, as base resins for chemically amplified resists, base resins containing a plurality of structural units are now used in order to improve lithography properties and the like.
For example, in the case of using a positive-type resist, a base resin is typically used which includes a structural unit having an acid dissociable, dissolution inhibiting group, the group dissociating under action of an acid generated from an acid generator, and further includes a structural unit having a polar group such as a hydroxyl group and a structural unit having a lactone structure. Of these structural units, the structural unit having a lactone structure is generally considered to contribute to the improvement of the adhesion of the resist film with a substrate, the improvement of compatibility with an alkali developing solution, and the improvement of lithography properties.
On the other hand, as acid generators usable in a chemically-amplified resist, various types have been proposed including, for example, onium salt-based acid generators such as iodonium salts and sulfonium salts; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators.
Currently, as the acid generator component for a chemically amplified resist, an onium salt-based acid generator containing an onium ion such as triphenylsulfonium as the cation moiety is used. As an anion moiety of the onium salt-based acid generator, an alkylsulfonate ion or a fluorinated alkylsulfonate ion in which a part or all of the hydrogen atoms of the alkyl group within the alkylsulfonate ion are substituted with fluorine atoms is used (for example, see Patent Document 3).